This project will obtain basic information about the reflection of ultrasound from structures within the human heart and from blood which will be used to improve the usefulness of diagnosis procedures using reflected ultrasound. Difficulties are presently encountered in applying these techniques to all patients. We believe that these difficulties can be partially overcome by investigating the factors which govern the strength of reflected echoes. Once these are known, a better choice of operating parameters for ultrasonic equipment can be made. The results of this work will help in the application of existing commercial equipment as well as new equipment since these choices are open to all users of ultrasonic equipment. Tissues being measured include myocardium, endocardium, valves and blood. Measurements are made both in vivo and on freshly removed specimens. Variables for tissues include frequency, angle of incidence and scattering angle. Additional variables for blood are hematocrit, PH and velocity of flow. Quantitative results are obtained as reflection coefficients or scattering cross-sections. Preliminary results indicate that thin structures such as heart valves show resonance effects in the range of frequencies used in echO-cardiography, resulting in large signal strength variations. Correlation of heart wall echO-strength with structural features such as endocardial thickness and infarcts is under way.